Int. J. Environ. Res. Public Health 2015, 12, 14301-14311; doi:10.3390/ijerph121114301
OPEN ACCESS
International Journal of
Environmental Research and
Public Health
ISSN 1660-4601
www.mdpi.com/journal/ijerph
Article
Exposure to Air Ions in Indoor Environments: Experimental
Study with Healthy Adults
Peter Wallner 1, Michael Kundi 1, Michael Panny 1, Peter Tappler 2 and
Hans-Peter Hutter 1,*
1
2
Institute of Environmental Health, Center for Public Health, , Medical University Vienna,
Kinderspitalgasse 15, Vienna 1090, Austria; E-Mails: [email protected] (P.W.);
[email protected] (M.K.); [email protected] (M.P.)
Austrian Institute for Healthy and Ecological Building, Alserbachstraße 5, Vienna 1090, Austria;
E-Mail: [email protected]
* Author to whom correspondence should be addressed;
E-Mail: [email protected]; Tel.: +43-1-40160 (ext. 34930);
Fax: +43-1-40160-934903.
Academic Editor: Paul B. Tchounwou
Received: 18 June 2015 / Accepted: 5 November 2015 / Published: 10 November 2015
Abstract: Since the beginning of the 20th century there has been a scientific debate about
the potential effects of air ions on biological tissues, wellbeing and health. Effects on the
cardiovascular and respiratory system as well as on mental health have been described.
In recent years, there has been a renewed interest in this topic. In an experimental indoor
setting we conducted a double-blind cross-over trial to determine if higher levels of air
ions, generated by a special wall paint, affect cognitive performance, wellbeing, lung
function, and cardiovascular function. Twenty healthy non-smoking volunteers (10 female,
10 male) participated in the study. Levels of air ions, volatile organic compounds and
indoor climate factors were determined by standardized measurement procedures. Air ions
affected the autonomous nervous system (in terms of an increase of sympathetic activity
accompanied by a small decrease of vagal efferent activity): In the test room with higher
levels of air ions (2194/cm3 vs. 1038/cm3) a significantly higher low to high frequency
ratio of the electrocardiography (ECG) beat-to-beat interval spectrogram was found.
Furthermore, six of nine subtests of a cognitive performance test were solved better, three
of them statistically significant (verbal factor, reasoning, and perceptual speed), in the
Int. J. Environ. Res. Public Health 2015, 12
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room with higher ion concentration. There was no influence of air ions on lung function
and on wellbeing. Our results indicate slightly activating and cognitive performance
enhancing effects of a short-term exposure to higher indoor air ion concentrations.
Keywords: air ions; cognitive performance; heart rate variability; lung function; indoor
air; wellbeing
1. Introduction
Air ions are charged particles that are generated by cosmic radiation and radioactive decay in air
and ground [1,2]. They are also generated by waterfalls (Lenard effect), friction forces in storms and
by lightning [1,3,4]. Measurements of air ions in ambient air showed that concentrations of air ions are
varying significantly between different environments. A high concentration of air ions can be found for
example close to waterfalls with concentrations up to 105 ions/cm3 whereas in urban areas and indoor
environments the amounts drop to several hundred ions/cm3 or less [5–7].
The first observations of the existence of air ions in natural environments were reported at the end
of the 19th century [3]. For many decades there has been a debate about potential biological effects of
air ions and of indoor air ionizers. Some studies showed that higher concentrations of (negative) air
ions may have, inter alia, a positive influence on alertness and cognitive performance [8–10].
With regard to mood, no consistent influence of positive or negative air ions has been observed in other
studies [5]. However, there are indications that artificially produced higher concentrations of negative air
ions may be effective in the treatment of depressions and seasonal affective disorder [11,12].
A recent meta-analysis concluded that negative air ionization was associated with lower depression
ratings [5]. High densities of negative air ions resulted in a change in serotonin levels in the brains of
rats and mice [13–15]. Bailey and Charry [16], however, found no effect of exposure to air ions on the
concentration or turnover of serotonin in rats.
Whereas ionized waterfall aerosol had a beneficial effect on asthma symptoms, lung function, and
airway inflammation [6], a systematic Cochrane review stated [17] that room air ionizers did not
improve pulmonary function of patients with asthma. In a review of 23 studies (published from 1933 to
1993) Alexander et al. [18] found “no persuasive evidence” for effects of air ions on respiratory
function. They summarize, however, that some studies reported beneficial effects of negative air ions,
while other studies found mild adverse effects of positive ions [18]. Using ergometry in healthy male
subjects, sudden introduction or removal of negative air ions induced increases in ventilation rate,
breathing equivalent, and cardiac frequency [19]. Herrington [20] and Albrechtsen et al. [21] found no
effect on heart rate, whereas Yaglou et al. [22] suggested that their data indicate a normalizing effect
of air ions on pulse rate (and other physiological functions). Generally, it remains unclear, whether
effects are due to increased concentrations of negative air ions or to increased total ion levels.
In this study, effects of increased indoor levels of air ions on wellbeing, cognitive performance,
lung function, and cardiovascular parameters (heart rate variability) were investigated. The increase in
air ion concentrations was not achieved by an ionizer, but by a mineral based wall paint. The wall paint
under study was a development intended to counteract the depletion of ions indoors. While earlier
Int. J. Environ. Res. Public Health 2015, 12
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approaches to increase indoor ion concentration (e.g., by corona discharge) had the disadvantage to
create ozone the wall paint has no such shortcomings. The product was investigated concerning its
potential to generate air ions by the German Fraunhofer Institute of Building Physics [23].
2. Experimental Section
2.1. Participants and Procedure
A randomized double-blind crossover experiment on 20 healthy non-smoking volunteers
(10 female, 10 male; age groups 20–35y—5 male, 5 female and 40–55y—5 male, 5 female) was
carried out in summer 2010. Participants were recruited through snowball sampling.
In two experimental sessions of this field investigation each volunteer underwent the same
standardized program in each of two rooms. The experiment (with one volunteer per session) had a
duration of two hours, each of the two sessions on the same day of the week and at the same time of
the day, one week apart. Half of the volunteers started the program in room A, the other in room B.
Room B had higher air ion concentrations (see 2.2.). Participants were instructed to refrain from coffee
drinking and not to eat two hours before the experiment and to avoid heavy physical exercise.
Upon their arrival, the participants were instructed about the procedure. After spirometry they were
equipped with electrocardiography (ECG) electrodes and recorders. During the two hour session
participants started with a period of standardized activity (crossword puzzle) for 25 min. Then they
completed, in order, the Self Condition Scale by Nitsch (5 min) [24] followed by the general cognitive
performance test by Horn (subtests 1–4) (10 min) [25], again followed by the Self Condition Scale
(5 min). After that the second period of standardized activity (jigsaw puzzle) was initiated and lasted
55 min. In the next step the second part of the cognitive performance test by Horn (subtests 7–9, 13, 14)
(15 min) and the Self Condition Scale by Nitsch (5 min) was filled in. After leaving the test room
spirometry tests were performed again.
The reason for this order was that the participants should first adapt to the experimental situation
and relax by doing a crossword. We wanted to ensure to keep the participants busy with some simple
activities (puzzle) during the 2 h exposure in order to avoid boredom or stressful thoughts, etc., and to
maintain a relaxed and restorative living room situation. The puzzle was introduced to standardize the
activity and to keep the volunteers busy with a not too demanding task. The puzzles were 200-piece
pictures of animals.
A trained and well experienced study assistant was always present before and during the whole
experimental session. She directed the participants from outside of the room via intercom system (plus
camera), in order to minimize disturbance (noise, etc.) and for adherence to the schedule.
The volunteers were told that the study is about indoor air quality. All subjects gave their written
consent for inclusion before they participated in the study after being informed about the procedure
and potential risks in accordance with the standards of the Ethics Committee of the Medical University
of Vienna. We informed the subjects in writing that the investigations are non-invasive and pose no
health risks. The study was conducted in accordance with the Declaration of Helsinki and the protocol
was approved by the Ethics Committee of Vienna (377/2010).
Int. J. Environ. Res. Public Health 2015, 12
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2.2. Experimental Setting
The experiment was conducted in two identical rooms (A and B) in a flat of a tenant house in
Vienna, Austria. The building was not on a busy road with a Lden in the category 55 to 60 dB according
to the noise information system of the city of Vienna and the windows were to the back so that air
pollution and noise were attenuated (in addition sound insulating windows were mounted). The rooms
were furnished like typical living rooms; one room was painted with a newly developed wall painting
to reach a higher concentration of (negative) air ions (room B). There was no recognizable difference
between the rooms which could unblind the room with the special mineral interior wall and ceiling
paint with silicate binder (Ionit©, Baumit GmbH, Wopfing, Austria). The setting was similar to other
studies investigating effects of components of indoor air (e.g., [26]); however, the test rooms in our
chamber were not laboratory rooms but identically furnished rooms in an ordinary tenant building.
The mechanisms which lead to higher air ion concentrations have been investigated via
environmental scanning electron microscopy, atomic force microscopy, electrostatic force microscopy,
and Klevin force microscopy (see Supplementary Material).
2.3. Measurements of Indoor Air Parameters
Air ions, temperature, and humidity were monitored continuously approximately one meter above
floor level one hour before and during the tests. Air ions were measured with Ionometer IM806
(Umweltanalytik Holbach GmbH, Wadern, Germany), which counts the number of negative and
positive air ions. The measurement interval was 5 s. Results were presented as arithmetic means over
the testing period. Furthermore, carbon dioxide concentrations were determined by infrared absorption
with testo sensor 535 (testo GmbH, Vienna, Austria).
Volatile organic compounds (VOC) air samples were taken by using adsorption tubes containing a
special activated charcoal (Anasorb 747, SKC Limited, Eighty Four, PA, USA). Sample flow rates
were about two liters per minute. VOCs were extracted from activated carbon with 1 mL of CS2 and
analyzed by gas chromatography/mass spectrometry (Shimadzu QP 5000, Scientific Instrument
Services,Kyoto, Japan), using a 60 meter fused silica capillary column (HP-VOC) following the Austrian
Standard ÖNORM M 5700-2 [27]. As internal standards cyclooctane and toluene-d8 were used.
2.4. Cognitive Performance
Cognitive performance was tested by the general cognitive performance test by Horn [25], which is
based on Thurstone’s intelligence model. This model describes seven primary mental abilities as basis
of the human intelligence. From the test system nine subtests—verbal factor (1,2), reasoning (3,4),
space and closure (7–9) and perceptual speed (13,14)—with up to 40 items each were used. Subtest 1
and 2 are assessing verbal fluency and consist of 40 nouns each, with each noun containing a wrong
letter which has to be detected. In subtest 3 and 4, (ir)regularities in geometric figures, letters and
numbers have to be identified and a series must be completed in each of 40 items. Subtests 7, 8, and 9,
each consisting of 40 items, are focusing on spatial perception and closure. Subtest 7 tests spatial
rotation, subtest 8 and 9 consist of comparisons between symbols. Raw scores were transformed to C
scores (standardization to a mean of 5 and a standard deviation of 2).
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2.5. Wellbeing
Wellbeing was assessed by the self-condition scale by Nitsch [24]. With this standardized
questionnaire the subjects characterize their actual state by 19 attributes (6-step-scale, “does not apply
at all—apples fully”) which map motivation and strain. The items belong to six dimensions: readiness
for action, readiness for exertion, alertness, state of mood, tension/relaxation and recuperation.
2.6. Lung Function
Lung function of the participants was assessed by spirometry (Masterscope, Viasys Healthcare Inc.
San Diego, CA, USA) performed by a trained technician. The calibration of the spirometer was carried
out each morning prior to the experiments. Lung function tests were performed according to the
protocol of the American Thoracic Society [28]. Both volume (FVC, Forced Vital Capacity, FEV1,
Forced Expiratory Volume in the 1st second) and flow parameters (PEF, Peak Expiratory Flow,
MEF25, 50, 75, Maximum Expiratory Flow at 25%, 50% and 75% of the FVC and MMEF,
Mean Maximum Expiratory Flow) were measured and documented.
2.7. Heart Rate Variability (HRV)
With a portable ECG device heart rate and its variability was analysed. Volunteers were equipped
with Medilog© AR12 Holter ECG recorders (Schiller, Bar, Switzerland) weighing 75 g. The signal
was digitized with a sample rate of 4096 Hz. Recorded data were digitally stored on SD memory cards
and afterwards uploaded to a computer for analysis.
The continuous ECG recordings were visually inspected for artefacts and were analysed with the
program Medilog Darwin (Schiller, Linz, Austria). Data of all test persons were assembled into one
Excel® file and were then imported to Statistica 10.0 (StatSoft (Europe) GmbH, Hamburg, Germany)
for further analysis. Spectral analysis was performed in order to analyse the frequency components of
the beat-to-beat intervals by using fast Fourier transform with a window width of 128 points.
Non-normal beats like extrasystoles were excluded from the analyses. A 20 min period that was as
artifact free as possible within the time window 60 to 90 min after start was chosen for the
measurement of HRV.
The HF (high frequency: range 0.15–0.4 Hz) component of HRV represents mainly parasympathetic
activation of the autonomous nervous system, the LF (low frequency: range 0.04–0.15 Hz) component is
assumed to be influenced mainly by sympathetic activity (Task force of the European Society of
Cardiology and the North American Society of Pacing and Electrophysiology) [29].
2.8. Statistical Analyses
Data were evaluated by analysis of variance with two factors (sequence: A after B vs. B after A and
room type: A vs. B). Gender and age were included as covariates. Normality of residuals was tested by
Kolmogorov-Smirnov tests with Lilliefors’ p-values. Homogeneity of variances was tested by Bartlett
tests. Comparison of climate and air pollution parameters in room A and B was evaluated using
Mann-Whitney U tests. For all tests, p-values below 0.05 were considered significant.
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3. Results and Discussion
Twenty healthy volunteers, 10 men and 10 women, were included in the study. Average age was
36.5 years. Average concentrations (Table 1) of Volatile Organic Compounds (VOC), as indicator for
indoor air quality, were well below the guideline level for indoor environment (1 mg/m3) [30] and did
not differ significantly between the two test rooms. Average temperatures ranged between 25 °C and
26 °C, humidity between 46% and 48%, showing no significant difference between the two rooms as
was the case for CO2 levels that were between 400 and 800 ppm, well below the guideline value of
1000 ppm [30].
Indoor air ion concentrations were significantly higher in room B than in room A: Total air ion
concentration in room B was 2194 per cm3 versus 1038 per cm3 in room A; negative air ion
concentrations were 866 per cm3 (room B) vs. 367 per cm3 (room A); positive air ion concentrations
were 1328 per cm3 (room B) vs. 671 per cm3 (room A). An overview of the indoor air climate factors
and pollutants are given in Table 1.
Table 1. Indoor air climate factors (temperature, relative humidity), CO2, volatile organic
compounds (VOC), formaldehyde and air ions in rooms A and B (arithmetic means).
Factor
Temperature
Relative humidity
CO2
VOC total
Formaldehyde
Air ions total
negative
positive
Unit
°C
%
ppm
µg/m3
ppm
ions/cm3
ions/cm3
ions/cm3
Room A
25.8
48.0
648
312
0.05
1038
367
671
Room B
25.3
46.3
624
357
0.05
2194
866
1328
p-Value
0.724
0.085
0.244
0.554
0.937
<0.001
<0.001
<0.001
CO2: Carbon dioxide; VOC: Volatile organic compounds.
In summary, in room B with the higher air ion concentrations, subjects performed better in the
cognitive test (Horn’s test). There was no influence of air ions on wellbeing (Nitsch self condition scale)
and lung function. With regard to heart rate variability, in room B an increase of low frequency and a
decrease of high frequency components were observed, resulting in a significantly higher LF/HF ratio.
In six of nine subtests of the Horn test participants showed better performances in the room with
higher ion concentrations (room B) (Table 2). There were significant differences in the results of three
subtests (verbal factor, reasoning, and perceptual speed).
Results of spirometry are shown in Table 3. None of the measured lung function parameters showed
a significant difference between rooms. Also, differences between tests before and after the stay in the
test rooms were small and not significant.
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Table 2. Cognitive performance tested by Horn’s test. Means (SD) for rooms A and B (the
room with higher air ion concentration). Values are standardized C scores. Higher values
define a better cognitive performance. p-values from factor room type of analysis of variance.
Factor
Verbal Factor
Reasoning
Space & Closure
Perceptual Speed
Subtest
1
2
3
4
7
8
9
13
14
Room A
3.46 (0.51)
3.53 (0.41)
6.92 (1.95)
7.34 (1.84)
6.70 (2.29)
5.63 (0.66)
7.15 (1.09)
5.59 (2.17)
3.80 (2.18)
Room B
3.24 (0.45)
3.86 (0.37)
7.51 (1.67)
7.16 (1.55)
6.84 (2.32)
5.87 (0.90)
7.07 (1.41)
6.73 (2.39)
4.10 (1.89)
p-Value
0.130
<0.001
0.008
0.264
0.428
0.102
0.816
0.042
0.481
Table 3. Results of ANOVA of spirometric findings.
Parameter
Unit
FVC
FEV1
PEF
MEF75
MEF50
MEF25
MMEF
mL
mL
mL/s
mL/s
mL/s
mL/s
mL/s
Room (A vs. B)
p-value
0.698
0.109
0.731
0.075
0.244
0.536
0.511
Before vs. After
p-value
0.600
0.126
0.289
0.274
0.988
0.307
0.448
Difference in Trend (A vs. B)
p-value
0.919
0.272
0.675
0.778
0.357
0.464
0.519
FVC: Forced Vital Capacity; FEV1: Forced Expiratory Volume in the 1st second; PEF: Peak Expiratory
Flow; MEF25, 50, 75: Maximum expiratory flow at 25, 50 and 75% of FVC; MMEF: Mean maximum
expiratory flow.
With regard to heart rate variability (HRV), a significant difference (p = 0.007) in the ratio of low
frequency (LF) to high frequency (HF) components was found between the two rooms. In room B
(higher air ion concentrations) an increase of the low-frequency (LF) and a decrease of high-frequency
(HF) components were observed, resulting in a significantly higher LF/HF ratio (Figure 1).
Effects of exposure to air ions are still a matter of debate. In recent years, there has been a renewed
interest in this topic [2,5,6,18]. The aim of our randomized, double-blind, crossover study was to
evaluate acute effects of increased concentrations of air ions indoors on wellbeing, cardiovascular
function, lung function and cognitive performance. Air ionization (in one of two rooms) was not
produced by an ioniser (which may have adverse side effects from increasing ozone levels) but by
means of a newly developed wall paint. The resulting air ion concentrations were lower than the
concentrations measured close to ionisers or waterfalls but still much higher than typically found in
urban indoor environments.
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Figure 1. Means and confidence interval of log ratio of the low to the high frequency
component (LF/HF) during 20 min standardized activity while seated in room A and B.
To our knowledge, this was the first study evaluating short term effects of indoor air ion
concentrations on HRV in humans. With regard to the LF/HF ratio, which is often suggested to represent
sympatho-vagal balance, we found a higher ratio in the room with higher air ion concentration.
The effect on HRV may indicate that air ions affected the sympatho-vagal balance which may be due to
either a slightly higher sympathetic activity or a slightly diminished vagal activity or both.
This effect on the cardiovascular system could be responsible for the better cognitive performance
(in most subtests and with statistical significance in three subtests), as Murray and Russoniello [31]
demonstrated that a moderate level of arousal based on increased sympathetic nervous system activity
was associated with an improved cognitive performance. But it is also possible that these observed
effects are due to independent pathways and consequences of more basic interactions of air ions with
body tissues.
In a study on rats, negative air ions were also found to modulate the regulation of autonomic
nervous system activity and to influence HRV [32].
In accordance with the conclusions from a recent review we found no effects of air ions on lung
function. We also found no influence on wellbeing of test persons which might be related to the short
duration of two hours only.
Taking into account that the experiment was conducted under a “real life situation” (identical living
rooms as test rooms) while controlling for the most important indoor air quality factors, we think that
this setting is a strength of the study and together with the double-blind condition might serve as a new
approach in the evaluation of indoor air ions. A limitation is the conduction during one season
(summer) only, because physiological as well as psychological function may vary over the year.
Also we could not differentiate between effects of positive and negative air ions as the wall paint
increases both species. The study was powered to detect rather strong effects only. Therefore, more
subtle effects would afford larger sample sizes.
Int. J. Environ. Res. Public Health 2015, 12
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4. Conclusions
The present study investigated short-term effects of air ions on physiological and psychological
parameters. The results of the presented study do not provide information about any further
development of physiological and psychological regulatory mechanisms while being chronically
exposed to higher air ions levels.
In our experiments, the elevated air ion levels were produced by a special wall paint. As this is a
new method to generate air ions, further studies on the topic with this method are warranted.
Acknowledgments
We want to thank Brigitte Piegler, Karin Trimmel, Claudia Schmöger and Jürgen Lorenz for their
assistance. Furthermore we grateful thank H. Plank, Institute for Electron Microscopy and Fine
Structure Research (FELMI), Graz University of Technology for his input. The study was financially
supported by Baumit Beteiligungen Gmbh, Wopfing 156, 2754 Waldegg, Austria.
Author Contributions
Peter Wallner, Michael Panny, Peter Tappler and Hans-Peter Hutter performed the experiments and
analysed the data. Peter Wallner, Michael Kundi and Hans-Peter Hutter designed the experiments and
wrote the paper. All authors read and approved the final manuscript.
Conflicts of Interest
The authors declare no conflicts of interest.
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